Iron tungsten coating formulations and processes

Abstract

An electrolyte solution for iron-tungsten plating is prepared by dissolving in an aqueous medium a divalent iron salt (e.g., iron (II) sulfate) and an alkali metal citrate (e.g., sodium citrate, potassium citrate, or other alkali metal citrate) to form a first solution, dissolving in the first solution a tungstate salt (e.g., sodium tungstate, potassium tungstate, or other potassium tungstate) to form a second solution, and dissolving in the second solution a citric acid to form the electrolyte solution. An iron-tungsten coating is formed on a substrate using the electrolyte solution by passing a current between a cathode and an anode through the electrolyte solution to deposit iron and tungsten on the substrate.

What is claimed is: 
     
       1. A method for plating a substrate using an electrolyte solution, the method comprising:
 preparing the electrolyte solution consisting of an aqueous medium; a divalent iron salt consisting of iron (II) sulfate, iron (II) halide, iron (II) nitrate, iron (II) acetate, or iron (II) perchlorate; an alkali metal citrate; a tungstate salt consisting of an alkali metal tungstate; a citric acid; and sodium hydroxide, potassium hydroxide, sulfuric acid, or a combination thereof by:
 dissolving in the aqueous medium, the divalent iron salt in an amount ranging from about 0.05 to about 0.5 mol per liter of the electrolyte solution and the alkali metal citrate in an amount ranging from about 0.05 to about 2 mol per liter of the electrolyte solution to form a first solution; 
 dissolving in the first solution the tungstate salt in an amount ranging from about 0.1 to about 1.5 mol per liter of the electrolyte solution to form a second solution; and 
 dissolving in the second solution the citric acid in an amount ranging from about 0.01 to about 1 mol per liter of the electrolyte solution to form the electrolyte solution; 
 
 passing a current between a cathode and an anode through the electrolyte solution to deposit iron and tungsten on the substrate; 
 forming a coating layer comprising an alloy of iron and tungsten having a tungsten content ranging from about 5 to about 18 At % or about 28 to about 40 At % when the pH of the electrolyte solution is maintained at about 3 to about 7; or 
 forming a coating layer comprising an alloy of iron and tungsten having a tungsten content ranging from about 18 to about 28 At % when the pH of the electrolyte solution is maintained at about 7 to about 12. 
 
     
     
       2. The method of  claim 1 , wherein:
 the step of dissolving the divalent iron salt and the alkali metal citrate comprises dissolving iron (II) sulfate in an amount ranging from about 0.05 to about 0.2 mol per liter of the electrolyte solution and sodium citrate or potassium citrate in an amount ranging from about 0.15 to about 0.5 mol per liter of the electrolyte solution; 
 the step of dissolving the tungstate salt comprises dissolving sodium tungstate in an amount ranging from about 0.15 to about 0.5 mol per liter of the electrolyte solution; and 
 the step of dissolving the citric acid comprises dissolving the citric acid in an amount ranging from about 0.02 to about 0.5 mol per liter of the electrolyte solution. 
 
     
     
       3. The method of  claim 1 , wherein the step of passing the current is performed using a carbonaceous anode, a graphite anode, a platinum anode, or a platinized titanium anode to deposit iron and tungsten on the substrate comprising a steel substrate, a copper substrate, a brass substrate, a copper-coated substrate, a nickel-coated substrate, or a combination thereof. 
     
     
       4. The method of  claim 1 , wherein the step of passing the current comprises applying a direct current having a current density ranging from about 0.002 to about 0.04 A/cm 2  to form the coating layer comprising an alloy of iron and tungsten having a tungsten content ranging from about 18 to about 28 At %. 
     
     
       5. The method of  claim 1 , wherein the step of passing the current comprises applying a direct current having a current density ranging from about 0.05 to about 0.1 A/cm 2  to form the coating layer comprising an alloy of iron and tungsten having a tungsten content ranging from about 5 to about 18 At % or about 28 to about 40 At %. 
     
     
       6. The method of  claim 1 , wherein the step of dissolving the tungstate salt comprises dissolving the tungstate salt in an amount ranging from about 0.3 to about 0.45 mol per liter of the electrolyte solution to form the coating layer comprising an alloy of iron and tungsten having a tungsten content ranging from about 18 to about 28 At %. 
     
     
       7. The method of  claim 1 , wherein the step of dissolving the tungstate salt comprises dissolving the tungstate salt in an amount ranging from about 0.1 to about 0.3 mol per liter of the electrolyte solution to form the coating layer comprising an alloy of iron and tungsten having a tungsten content ranging from about 5 to about 18 At % or about 28 to about 40 At %. 
     
     
       8. The method of  claim 1 , further comprising maintaining a temperature of about 50 to about 70° C. during the step of passing the current to form the coating layer comprising an alloy of iron and tungsten having a tungsten content ranging from about 18 to about 28 At %. 
     
     
       9. The method of  claim 1 , further comprising maintaining a temperature of about 20 to about 50° C. during the step of passing the current to form the coating layer comprising an alloy of iron and tungsten having a tungsten content ranging from about 5 to about 18 At % or about 28 to about 40 At %. 
     
     
       10. The method of  claim 1 , wherein the step of dissolving the citric acid comprises dissolving the citric acid in an amount ranging from about 0.05 to about 0.25 mol per liter of the electrolyte solution to form the coating layer comprising an alloy of iron and tungsten having a tungsten content ranging from about 18 to about 28 At %. 
     
     
       11. The method of  claim 1 , wherein the step of dissolving the citric acid comprises dissolving the citric acid in an amount ranging from about 0.25 to about 0.5 mol per liter of the electrolyte solution to form the coating layer comprising an alloy of iron and tungsten having a tungsten content ranging from about 5 to about 18 At % or about 28 to about 40 At %. 
     
     
       12. The method of  claim 1 , wherein the step of passing the current comprises:
 applying a first direct or pulsed current having a first current density during at least one time interval to form the coating layer having a tungsten content ranging from about 5 to about 18 At % or about 28 to about 40 At %; or 
 applying a second direct or pulsed current having a second current density during at least one second time interval to form the coating layer having a tungsten content ranging from about 18 to about 28 At %. 
 
     
     
       13. The method of  claim 1 , wherein the step of passing the current forms a plurality of iron-tungsten alloy coating layers comprising at least one coating layer comprising an alloy of iron and tungsten having a tungsten content ranging from about 5 to about 18 At % or about 28 to about 40 At % and at least one coating layer comprising an alloy of iron and tungsten having a tungsten content ranging from about 18 to about 28 At %. 
     
     
       14. The method of  claim 13 , wherein the step of passing the current comprises:
 applying a first direct or pulsed current having a first current density during at least one time interval to form the coating layer having a tungsten content ranging from about 5 to about 18 At % or about 28 to about 40 At %; and 
 applying a second direct or pulsed current having a second current density during at least one second time interval to form the coating layer having a tungsten content ranging from about 18 to about 28 At %. 
 
     
     
       15. The method of  claim 13 , wherein a thickness of the at least one coating layer comprising an alloy of iron and tungsten having a tungsten content ranging from about 5 to about 18 At % is equal to a thickness of the at least one coating layer comprising an alloy of iron and tungsten having a tungsten content ranging from about 18 to about 28 At %. 
     
     
       16. The method of  claim 13 , wherein a thickness of the at least one coating layer comprising an alloy of iron and tungsten having a tungsten content ranging from about 5 to about 18 At % is different from a thickness of the at least one coating layer comprising an alloy of iron and tungsten having a tungsten content ranging from about 18 to about 28 At %. 
     
     
       17. The method of  claim 1 , wherein the divalent iron salt consists of iron (II) sulfate heptahydrate, the alkali metal citrate consists of sodium citrate dihydrate, and the tungstate salt consists of sodium tungstate dihydrate. 
     
     
       18. The method of  claim 1 , wherein the substrate comprises a Hull cell panel. 
     
     
       19. The method of  claim 1 , wherein the coating layer comprising an alloy of iron and tungsten having a tungsten content ranging from about 18 to about 28 At % is formed, and the pH of the electrolyte solution is maintained at about 7.5. 
     
     
       20. The method of  claim 1 , wherein the coating layer comprising an alloy of iron and tungsten having a tungsten content ranging from about 5 to about 18 At % or about 28 to about 40 At % is formed, and the pH of the electrolyte solution is maintained at about 3 or about 5.